One leg cycling alterations

david.123
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One leg cycling alterations

Postby david.123 » Thu Feb 22, 2018 10:12 am

I'd like to alter my electric bike so I can cycle using one leg. I've been having severe knee trouble so have bought an electric bike and would like to take the right pedal off and cycle with just the left leg using a cleat. The challenge is how to support the right leg without a pedal to rest on (even passive movement on the pedal causes issues)? Any bright ideas for a quick and easy solution would be much appreciated!

rooftop
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Re: One leg cycling alterations

Postby rooftop » Thu Feb 22, 2018 12:38 pm

You might be able to buy a foot peg that clamps onto the frame tubing somewhere - motorcyclists use them on engine guards/crash bars.

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Re: One leg cycling alterations

Postby Jmuzz » Thu Feb 22, 2018 1:49 pm

Search highway pegs and see if any have suitable mounting for the frame.

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Alex Simmons/RST
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Re: One leg cycling alterations

Postby Alex Simmons/RST » Thu Feb 22, 2018 4:55 pm

or a very short crank like some paracyclists use.

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bychosis
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Re: One leg cycling alterations

Postby bychosis » Thu Feb 22, 2018 5:16 pm

It’s goig to be more difficult being on the drive side. Even removing the crank will be difficult. Other than a frame based peg of some sort I can’t think of anything.
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MattyK
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Re: One leg cycling alterations

Postby MattyK » Fri Feb 23, 2018 10:10 am

What bike? (specifically what crankset and bottom bracket?)

If you have (or retrofitted) a square taper BB, then I can envisage replacing the right crank retainer bolt with some adaptor* that is headed with a female thread into which you could screw a pedal.

Something like:
Image
PLUS
Image
PLUS
Image

I'm not sure it would be comfortable at that height though.

*M8 x 1mm Male to 9/16'-20 TPI Female. I doubt such a thing exists but any machine shop should be able to make one, if they have the right tap.

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ValleyForge
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Re: One leg cycling alterations

Postby ValleyForge » Fri Feb 23, 2018 11:53 am

[quote="MattyK"]What bike? (specifically what crankset and bottom bracket?)

If you have (or retrofitted) a square taper BB, then I can envisage replacing the right crank retainer bolt with some adaptor* that is headed with a female thread into which you could screw a pedal.
[quote]
Great idea - but given it's the drive side - I think it's in the too hard basket.
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MattyK
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Re: One leg cycling alterations

Postby MattyK » Fri Feb 23, 2018 11:57 am

ValleyForge wrote:
MattyK wrote:What bike? (specifically what crankset and bottom bracket?)

If you have (or retrofitted) a square taper BB, then I can envisage replacing the right crank retainer bolt with some adaptor* that is headed with a female thread into which you could screw a pedal.

Great idea - but given it's the drive side - I think it's in the too hard basket.

I don't believe that would make it any harder.
Image

Worst case you could cut the crank arm off but I reckon it would be far enough away to not be a problem.

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ValleyForge
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Re: One leg cycling alterations

Postby ValleyForge » Fri Feb 23, 2018 12:11 pm

MattyK wrote:
ValleyForge wrote:
MattyK wrote:What bike? (specifically what crankset and bottom bracket?)

If you have (or retrofitted) a square taper BB, then I can envisage replacing the right crank retainer bolt with some adaptor* that is headed with a female thread into which you could screw a pedal.

Great idea - but given it's the drive side - I think it's in the too hard basket.

I don't believe that would make it any harder.
Image

Worst case you could cut the crank arm off but I reckon it would be far enough away to not be a problem.

I reckon you would need to. Else you will have a fair extension on the female fitting to clear the crank arm.
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Re: One leg cycling alterations

Postby find_bruce » Fri Feb 23, 2018 1:11 pm

MattyK wrote:*M8 x 1mm Male to 9/16'-20 TPI Female. I doubt such a thing exists but any machine shop should be able to make one, if they have the right tap.

The head on an m8 crank bolt is 14mm ~9/16. The nut for a 9/16 bolt is usually 13/16, ~21mm, which may not fit inside the crank. Plus a 175% step in the wrong direction means you need to be careful to leave enough meat in the middle to transition from one to the other.

As you say it also may not be comfortable to have a pedal at the level of the bottom bracket.

If David can cope with a small revolution, I would look at drilling a new pedal thread to give a very short crank as Alex suggested.

If that doesn't work for David I would cut the crank off to avoid getting whacked by it and look at mounting a footpeg at a suitable position from the downtube.

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Re: One leg cycling alterations

Postby MattyK » Fri Feb 23, 2018 1:32 pm

find_bruce wrote:
MattyK wrote:*M8 x 1mm Male to 9/16'-20 TPI Female. I doubt such a thing exists but any machine shop should be able to make one, if they have the right tap.

The head on an m8 crank bolt is 14mm ~9/16. The nut for a 9/16 bolt is usually 13/16, ~21mm, which may not fit inside the crank. Plus a 175% step in the wrong direction means you need to be careful to leave enough meat in the middle to transition from one to the other.

Look at my first pic above. That bolt looks much bigger than 14mm under the head.
Of course it would have to be custom made anyway, so the details like that would be figured out at the design stage.

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Re: One leg cycling alterations

Postby Duck! » Fri Feb 23, 2018 11:59 pm

Although not falling under the "quick and easy" criteria, I would suggest getting to the root of the knee problem and addressing that rather than trying to skirt around the issue with solutions that, even with the assistance of a motor unit, concentrate all stresses on the other leg, potentially blowing that up too.

There's the old saying, "use it or lose it", and that's valid to several extents, and that applies to joint mobility as much as anything else. While high-level joint mobility may cause problems, limiting use of the joint can be just as harmful for joint health in the long term. Therefore I'd suggest using a short crank, around 150mm, which will still allow both legs to do a more equal portion of the work, and maintain mobility in the troublesome knee, but reduce the stress imposed by a larger range of movement. It would in all probability be better for the knee than removing almost all movement.
I had a thought, but it got run over as it crossed my mind.

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Alex Simmons/RST
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Re: One leg cycling alterations

Postby Alex Simmons/RST » Sat Feb 24, 2018 11:18 am

Duck! wrote:Although not falling under the "quick and easy" criteria, I would suggest getting to the root of the knee problem and addressing that rather than trying to skirt around the issue with solutions that, even with the assistance of a motor unit, concentrate all stresses on the other leg, potentially blowing that up too.

There's the old saying, "use it or lose it", and that's valid to several extents, and that applies to joint mobility as much as anything else. While high-level joint mobility may cause problems, limiting use of the joint can be just as harmful for joint health in the long term. Therefore I'd suggest using a short crank, around 150mm, which will still allow both legs to do a more equal portion of the work, and maintain mobility in the troublesome knee, but reduce the stress imposed by a larger range of movement. It would in all probability be better for the knee than removing almost all movement.

While we don't know the extent of the issues the OP faces, for reference when I started back after amputation and had limited knee flexion on my prothesis leg side, I started with a 100mm crank a mate made for me (I was already using square taper cranks so finding and hacking down a crank arm wasn't that hard). That meant I could at least ride.

Eventually as I improved I migrated to a 150mm crank arm and eventually regular 170mm crank arm. I also had a set of adjustable length SRM cranks on my indoor trainer bike which I could get down to 145mm and adjust as I went.

I had a big advantage of it being left side though. Much harder on the drive side.

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